Activated clotting time also known as activated coagulation time is a test of coagulation

Coagulation

Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...

.

The ACT test is used to monitor the effect of high-dose heparin

Heparin

Heparin , also known as unfractionated heparin, a highly sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule...

 before, during, and shortly after surgeries that require intense anticoagulant

Anticoagulant

An anticoagulant is a substance that prevents coagulation of blood. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders. Some anticoagulants are used in medical equipment, such as test tubes, blood transfusion bags, and renal dialysis...

 administration, such as cardiac bypass surgery, cardiac angioplasty, and dialysis

Dialysis

In medicine, dialysis is a process for removing waste and excess water from the blood, and is primarily used to provide an artificial replacement for lost kidney function in people with renal failure...

. It is ordered in situations where the partial thromboplastin time

Partial thromboplastin time

The partial thromboplastin time or activated partial thromboplastin time is a performance indicator measuring the efficacy of both the "intrinsic" and the common coagulation pathways...

(PTT) test is not clinically useful or takes too long.